Drill pipe stabilizing apparatus



p 30, 1969 E. HORTON 3,469,820

DRILL PIPE STABILIZING APPARATUS Filed July 5, 1967 5 Shectx-Sheet 1INVENTOR EDWARD E HORTON Sept. 30, 1969 E. E. HORTON DRILL PIPESTABILIZING APPARATUS 5 Sheets-$heet 1'.

Filed July 5. 1967 Sept. 30, 1969 a. E. HCRTON 3,469,

DRILL PIPE smsxmzmc APPARATUS Filed July 5, 1967 5 Sheets-Sheet Z 5a i l1 v PUMP 44 54 44 \C lqo POSITION SIGNAL SIGNAL MIXER 1 22 I SIGNAL -1022a GAIN v as v CHANGE SIGNAL M98 /2 96 SIGN FIG. 6

p 30, 1969 E. E. HORTON 3,469,820

DRILL PIPE STABILiZING APPARATUS Filed July 5, 1967 5 Sheets-Sheet 4PRIOR ART I PRIOR ART Sept. 30, 1969 E. E. HORTON 3,469,820

DRILL PIPE STABILIZING APPARATUS Filed July 5, 1967 5 Sheets-Sheet sUnited States Patent US. Cl. 254-172 7 Claims ABSTRACT OF THE DISCLOSUREA construction for use in an offshore drilling operation for maintainingthe vertical location of a drill pipe stable with respect to the oceanfloor even though its floating support platform is subject to waveaction. The drill pipe is supported by cables depending from a travelingcrown block which is in turn primarily supported with respect to theplatform by a plurality of pressurized air cylinders and secondarily bya plurality of hydraulic cylinders. The hydraulic cylinders are doubleacting and provide motive power synchronized with ship heave to move thecrown block relative to the platform so it remains stationary relativeto the ocean floor. The synchronization power is controlled by a traveldetecting accelerometer.

This invention relates to apparatus for stabilizing the tension andcompression forces acting on a drill pipe suspended from a floatingvessel during an offshore drilling operation. The art of conductingdrilling operations from ships and stations at points over the bed ofthe ocean has become increasingly active in recent years. When thedrilling is commenced at great depths, it is impractical to stabilizethe drilling platform with members extending to the ocean floor. Suchdrilling stations or platforms therefor are subject to the wave actionsof the sea. Although certain measures are available to reduce the effectof this wave action through ship design and buoy systems, the principaleffect of this wave action is always present. Such heaving action causesthe drill pipe and drill bit to be alternately pulled upwardly from thedrilling area as the platform rises and dashes the bit against thebottom of the boring as the platform drops. This invention providesapparatus for mounting the drill pipe to the platform in a manner tomaintain stability with respect to the ocean floor by substantiallyisolating the wave action from the drill pipe.

A principal object of the invention is to provide a crown block supportmeans for the drill pipe which means includes apparatus causing thecrown block to remain relatively fixed with respect to the ocean flooras its mounting platform heaves.

Another object of the invention is to provide a crown block supportingmeans which utilizes pressurized air as a primary support means andhydraulic fluid as both a secondary support means and a power means.

A further object of the invention is to provide a crown supporting meansblock which quickly compensates for wave action through a hydraulicpower system controlled by an accelerometer detector which anticipatesthis wave action.

A still further object of the invention is to provide a sheave supportsystem for a cable supported crown block having minimum sheave rotationwhen corrective motions are necessary.

Another object of the invention is to provide a crown block which isadjustable to proportionately compensate for only a segment of platformheave when the wave action is so severe that it cannot be fullycompensated because of physical limitations in the supporting derrick.

These and other objects of the invention will become more apparent tothose skilled in the art by reference to the following detaileddescription when viewed in light of the accompanying drawings, wherein:

FIGURE 1 is a front elevational view of the invention;

FIGURE 2 is a side elevational view of the invention;

FIGURE 3 is a perspective view of the crown block assembly;

FIGURE 4 is a front elevational view of the crown block assembly;

FIGURE 5 is a schematic of the crown block air and hydraulic system;

FIGURE 6 is a schematic of the crown block control system;

FIGURES 7a and 7b are a schematic of a prior art sheave support systemin different positions;

FIGURES 7c and 7d are a schematic of the instant sheave support systemin two different positions, and

FIGURES 8a, b and c are diagrammatic elevational views of the ship inthree different positions.

Referring now to the drawings, wherein like numerals indicate likeparts, the numeral 10 indicates a ship or other fioatable platform whichhas a derrick l2 rigidly mounted on its deck. The derrick is of a typewhich is well known in the art and has a water table platform 14 at itsupper end and a working board 16 therebelow. The derrick is used tosupport a drill string 18 by means of a travel block 20 and a crownblock assembly 22 over and through which pass the cables or lines 23-.In order to prevent twisting of the lines 23, outwardly extending arms24 and 24 are provided to slidably engage a pair of guide rails 26 and26'.

Assembly 22 is located within a derrick superstructure 28 and issupported by the water table platform 14. The superstructure comprises aframework 30 having vertical legs 32 which are rigidly braced bydiagonal beams 34. The crown block assembly 22 includes a pair ofopposed horizontal bars 36 which rotatably support a plurality of crownblock sheaves 38. The assembly 22 is supported within the framework by aplurality of vertically disposed air pistons 41. A plurality of rollers40 are mounted on the assembly and engage the inner corners of the legs32 to thus permit relative movement between the assembly 22 and theframework 30.

The pistons 41 have their rods 42 secured to cross bars 36 and theircylindrical portions 46 to the table 14 via pins 47. The air cylindersare communicated to pressurized air storage tanks or flasks 50 locatedon the working board 16 by air pressure lines 48. The pressurized airprovides a resilient means of supporting the major portion of the crownblock load. In addition to its weight, the load includes the suspendeddrill string 18.

The crown block assembly is further supported by a plurality of doubleacting hydraulic jacks 54. First rods 52 of the jack are slidablyreceived through the upper end of cylinders 56 and are secured to bar 36by pin connections 47. The base of cylinders 56 are connected to watertable 14 also by pin connectors although the lower ends of cylinders 56have balance rods 52', which are not connected to any part of theapparatus. The hydraulic jacks can move the assembly to any selectedposition intermediate the vertical length of framework 30.

The double acting hydraulic pistons 54 are used not only as a secondarysupport means for taking up load difference not taken up by the airpistons 44 but primarily provide the means for moving the crown block incompensating synchronization with the vertical motion of the ship. It isadvantageous to use a double-acting, double-ended jack with theexpansion chambers interconnected since the displaced volume of fluidfrom the contrasting side of the cylinder will equal the increase involume expanding chamber. As best seen in FIGURE 5, opposite ends of thecylinder 56 are communicated by hydraulic lines 58, 58' to a variabledisplacement pump 60.

In the event of a sudden change in crown block load due to a suddenbreak in the drill string or fracture in either the air or hydraulicsystems, a dash pot 62 (FIG- URE 4) is provided on the work table withits dash pot rod 64 secured to the bar 36. Although not shown, theinterior of the dash pot cylinder is grooved to allow adequate velocityof the crown block at the middle of its vertical movement and controlleddeceleration at the end of it. A spring biased relief valve 66 (FIGURE5) will operate upon a sudden load change to pass fluid to the lowpressure side of the hydraulic system and thus simultaneously transferthe load to the dash pots 62. During normal operation, the dash pots arepassive and have a negligible effect.

As briefly mentioned above, the line 23 passes about the crown sheaves38. As best seen in FIGURES 3 and 4, an idler sheave 68 is rotatablysupported between rigid web plates 70. The idler sheave 68 supports thedead line portiton 72 of the line 23. An idler sheave 74 is similarlydisposed on the opposite end of the work table 14 between the web plates76 and supports the fast line portion 78 of the line 23. A schematic ofthe instant sheave support system is shown in FIGURES 7c and 7d anddiscloses that the dead line 72 is secured to the derrick floor whilethe fast line 78 passes around a fast sheave 80 on the derrick floor andthence to a draw works drum (not shown) which maintains a constantpreselected tension therein. The purpose of the idler sheaves is tominimize rotation of the traveling block sheaves and the crown blocksheaves to thus reduce line and sheave wear. In FIGURES 7a and 7b, asheave support system is shown without the idler sheaves. It can be seenwhen the ship moves down from the FIG- URE 7a to the FIGURE 7b position,the compensating vertical movement of the crown block causes arelatively large partial rotation of the crown and travel sheaves. Thesheave support system (FIGURES 7c and 7d) utilizes the idler sheavesdisposed on the water table at an elevation substantially equal to themidpoint of the crown sheaves vertical movement limits. The portion ofthe dead line and the fast line between the idler sheave and crownsheave are indicated by the numerals 72 and 78' respectively. When theship moves from the FIGURE 70 to the FIGURE 7d position the idlersheaves move downwardly with the ship while the crown sheaves arecompensated upwardly. The line portions 72 and 78 are thus moved out oftheir substantially horizontal positions to provide a component of theincreased dead line and fast line legths. In other words, in FIGURE 7d,the increase in distance between the derrick floor and the crown sheavesis supplied partly by a swinging movement of the dead line and fast lineportions 72' and 78' and partially by longitudinal lengthening of thedead and fast lines 72, 78 whereas in FIGURE 7b, the increase indistance is wholly supplied by a longitudinal lengthening of the deadand fast lines 72, 78.

From the foregoing discussion, it is apparent that the reduced rotationof the crown and travel sheaves gained by the use of idler sheaves willresult in minimum line and sheave wear. It is also seen that since thedead line and fast line come off of the crown sheaves on the horizontal,their loads are not supported by the air and hydraulic pistons of thecrown block assembly.

For effective operation the speed of crown block compensation must besynchronized vw'th the speed of the ships heave 14. For these purposes acontrol system as shown in FIGURE 6 is provided. An accelerometer 82 onthe crown block 22 senses vertical motion and transmits an electricsignal to a servo valve 84. The signal will be positive or negativedepending on the direction of the vertical movement. The servo controlsthe output of a hydraulic accumulator 86 and directs it 4 through eitherof the lines or 90' to the valve 88 to determine flow of the pump 60through one of the two lines 58, 58'.

Drift of the crown block from its mid position is prevented by the useof a conventional electrical signal device wherein a displacement signalis originated at 94. The said displacement signal is proportional to thedistance the crown block is from the mid-point and acts as a smalloverride to keep the crown block centered.

During heavy seas, the ship heave motion may exceed the allowable travelof the crown block and it is therefore desirable to compensate for onlya portion of the heave. To accomplish this, .a second accelerometer 96is provided on the water table. The signal from the second accelerometerhas its sign reversed at 98. The water table signal is thus subtractedfrom the crown block signal at a signal mixer 100 and the differencewill then go to the servo valve 84. The amplification of the water tablesignal takes place at 102 and is adjustable by the operator. If theabsolute values of the two signals are equal, no compensation takesplace. If, for example, the water table signal is set at 80 percent ofthe crown block signal, the crown block is compensated only to 20percent.

The operating principles are best seen in FIGURES 8a, 8b and 80 whichdepict compensation of the crown block location during different stagesof ship hea-ve. The movements discussed will relate to movementsrelative to the sea floor unless otherwise specified.

During a mean position as shown in FIGURE 8a, the crown block 22 withits hook load is supported near its mid-point in the framework 30' bythe air pistons 44 and the hydraulic jacks 54. As long as the ship isstationary, the crown block will be stationary also. As the ship heavesupwardly to the FIGURE 8b position, the inertial force of the loadsupported by the air pistons 44 will resist upward movement and causeair compression in the cylinders 46. The natural resistance to upwardmovement, however, is lessened by the increasing pressure of the air,and the crown block will begin an upward travel. The accelerometer 82(FIGURE 6) will sense this travel and cause hydraulic fluid to flow intoupper chambers of cylinders 56 to maintain the crown block stationary.Similarly, when the ship moves downwardly to the FIGURE 80 position, anytendency of the crown block to move downwardly is sensed :by theaccelerometer 84 and hydraulic fluid is pumped to the lower chambers ofthe cylinders 56.

What has been set forth above is intended primarily as exemplary toenable those skilled in the art in the practice of the invention.

What is new and therefore desired to be protected by Letters Patent ofthe United States is:

1. Apparatus for maintaining a substantially fixed vertical location ofa drill pipe with respect to a bore through the sea floor underlying abody of water and which drill pipe is supported by a cable networksuspended from a framework mounted on a floating platform overlying saidbore, wherein the improvement comprises:

a sheave assembly mounted for vertical slidable movement in saidframework,

resilient support means between said framework and said assemblynormally supporting said assembly intermediate the vertical length ofsaid framework,

a vertically disposed expansion jack having one end connected to saidframework and its other end connect-ed to said assembly, said jackhaving first and second expansion chambers,

a source of pressurized fluid having a conduit system leading to saidfirst and second expansion chambers, and

control means causing said first chamber to expand and said secondchamber to contract when said platform moves toward the sea floor andcausing said second chamber to expand and said first chamber to contractwhen said platform moves away from said sea floor.

2. The invention described in claim 1 wherein said control meanscomprises an accelerometer movement sensing means which emanates anelectric signal when a vertical movement is sensed between said assemblyand said sea floor,

and hydraulic valve means responsive to said signal for communicatingone of said chambers to said source upon receiving said signal.

3. The invention as described in claim 2 wherein said accelerometermovement sensing means comprises an accelerometer resiliently mounted onsaid assembly for detecting a relative vertical movement between saidassembly and said bore,

said accelerometer emanating a positive or a negative electric signaldepending upon the direction of said movement,

a servo valve connected to said accelerometer having an input and firstand second outputs, a hydraulic accumulator on one side of said valveand a hydraulic pump on the other side of said valve,

said valve communicating fluid from said accumulator to said pumpthrough one of said outputs in re sponse to said positive electricsignal and through the other of said outputs in response to saidnegative electric signal,

whereby the output of said pump is directed to said first chamber whensaid signal is positive and to said second chamber when said signal isnegative.

4. The invention as described in claim 1 wherein said resilient supportmeans comprises at least one air cylinder mounted on said framework, apiston slidably received within said cylinder, and forming an airchamber there with, a piston rod connected at one end to said piston andat the other end to said assembly, and means to provide a preselectedpressure in said air chamber.

5. The invention as described in claim 2 including a secondaccelerometer provided on said platform which emanates a second electricsignal when a vertical movement is sensed between said platform and saidsea floor,

an amplifier connected to said second accelerometer,

a signal mixer connected between said first accelerometer and saidamplifier, said second accelerometer being connected to said signalmixer through said amplifier,

means for reversing the sign of said second electric signal whereby thesecond electric signal is subtracted from the first electric signal atsaid signal mixer whereby only a portion of said relative verticalmovement between said assembly and said sea floor will be compensated.

6. The invention as described in claim 1 wherein said sheave assemblycomprises:

a plurality of rotatable axially aligned crown sheaves mounted forvertical slidable movement in said framework;

a plurality of rotatable axially aligned travel sheaves verticallyspaced from said crown sheaves,

said travel sheaves lesser in quantity than said crown sheaves by one,

first and second idler sheaves rotatably mounted on said framework at anelevation substantially corresponding to the midpoint of said crownsheaves vertical travel range,

a cable having one end rigidly secured to a fixed point on saidplatform,

tension means mounted on said platform connected to the other end ofsaid cable for maintaining a constant tension in said cable,

said cable extending from said fixed point over said first idler sheave,alternately and successively around each of said crown sheaves and saidtravel sheaves and over said second idler sheave to said tension means.

7. The invention as described in claim 6 wherein said tension meanscomprises a cable payout drum.

References Cited UNITED STATES PATENTS 1,928,958 10/1933 Young 254-1902,961,216 11/1960 Blair 254-172 3,276,746 10/1966 Berne 254-1723,309,065 3/1967 Prudhomme 254-172 EVON C. BLUNK, Primary ExaminerHARVEY C. HORNSBY, Assistant Examiner U.S. Cl. X.R.

